Re: optimize file transfer in pg_upgrade

On Wed, Mar 5, 2025 at 2:43 PM Nathan Bossart <nathandbossart@gmail.com>
wrote:

> One other design point I wanted to bring up is whether we should bother
> generating a rollback script for the new "swap" mode.  In short, I'm
> wondering if it would be unreasonable to say that, just for this mode, once
> pg_upgrade enters the file transfer step, reverting to the old cluster
> requires restoring a backup.


I think that's a fair requirement. And like Robert, revert scripts make me
nervous.

* Anecdotally, I'm not sure I've ever actually seen pg_upgrade fail
> during or after file transfer, and I'm hoping to get some real data about
> that in the near future.  Has anyone else dealt with such a failure?


I've seen various failures, but they always get caught quite early.
Certainly early enough to easily abort, fix perms/mounts/etc., then retry.
I think your instinct is correct that this reversion is more trouble than
its worth. I don't think the pg_upgrade docs mention taking a backup, but
that's always step 0 in my playbook, and that's the rollback plan in the
unlikely event of failure.

Cheers,
Greg

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